1. Field of the Invention
The present invention relates to an apparatus and method adapted to controlling a motor. More particularly, the invention relates to an apparatus and method for precisely controlling a brushless direct current (DC) motor in relation to a mechanical tolerance.
This application claims the benefit of Korean Patent Application No. 10-2006-0003497, filed on Jan. 12, 2006, the subject matter of which is hereby incorporated by reference.
2. Description of the Related Art
Hard disk drives (HDDs) are commonly used within various host devices, such as personal computers (PCs), as data storage devices. In general operation, HDDs allow data to be written to and read from recording medium (e.g., a disk having a surface subject to variation in its magnetic properties) using a magnetic read/write head. Data is stored on conventional disks in terms of bits per inch (BPI)—a recording density defined in relation to the disk's rotational direction, and tracks per inch (TPI)—a recording density defined in relation to the disk's radial direction. Significant research and development efforts are currently being expended to increase data recording density according to both of these definitions. Additionally, commercial demands are increasing for increasingly small HDDs. The increasing miniaturization of HDDs, together with demands for higher data recording densities, require ever finer and more precise mechanisms within HDD structures.
Conventional HDDs commonly rotate constituent their disk(s) at a constant angular velocity using a brushless direct current (DC) motor. As the disk rotates, data is read from or written to it using a magnetic read/write head. As the rotational speed of the disk increases, a feedback sampling frequency used to read/write data must be correspondingly increased to preserve the precision of data access operations.
Conventionally, a spindle motor is used to rotate the disk of an HDD in a precise and well-controlled manner. This is often accomplished using a feedback signal derived from a back electromotive force generated by the spindle motor. This approach does not require the use of an additional sensor which reduces production costs. A speed estimation integral to the feedback control loop may be derived from a phase signal provided by a driving circuit associated with the motor. The phase signal may be generated as the back electromotive force generated by the motor passes a zero point and the corresponding phase of the back electromotive force changes accordingly. In the context of this approach, the phase of the back electromagnetic force will change in accordance with the maximum number of magnetic poles associated with the motor as it rotates the disk. Therefore, if the motor is synchronously controlled in relation to such phase changes, the resulting sampling rate will correspond to the motor's maximum number of magnetic poles during a given time period.
However, if the sampling frequency is increased, the resulting changes in the interval of magnetic poles due to the mechanical tolerance of a permanent magnet within the motor will negatively affect the system's performance. This causes a false error when the measured speed is used as a feedback signal to the controller, and thus, resonance may be generated in the spindle motor.